Media not supported (MP4, AVI)

Hi everybody. I have a new WD My Cloud Ex2 Ultra but cannot play any media.
Cell phone: doesn’t matter whether I access it via File Manager – Remote, or via My Cloud, all movies in MP4 or AVI cannot be played (“This file is not supported”).’
TV Philips: Installed DLNA but situation is the same, media files are not supported. I can see some JPG pics and play some music, that’s all.
No matter whether on local wi-fi or connecting via internet (in case of cell phone)…

Thanks for any advice.

Try a Media Player like VLC.